Alternator brush holder

ABSTRACT

A brush holder assembly for an alternator having a rotational axis includes a pair of brushes each having a contacting surface defining a width and a height, and each having a shunt wire extending laterally from the brush in the widthwise direction. The brush holder assembly includes a housing having first and second brush chambers, corresponding first and second wire cavities each defining a cavity height, and first and second slots respectively interposed between the corresponding chamber and cavity. The respective shunt wires extend through the first and second slots then through the first and second wire cavities. The cavity heights are each at least approximately 0.9 times the height of one of the brushes. The height of the first wire cavity is less than approximately 0.97 times ((A/2) plus B), wherein A is the brush height and B is the distance between the brushes.

BACKGROUND

The present invention relates generally to an alternator brush holderassembly and, more particularly, to improved reliability for a springtype brush assembly.

Dynamo electric machines such as generators, motors, and automotivealternators may include brushes that provide electrical communicationbetween a spinning rotor and other components of an electric machinecircuit. Brushes are typically composed of carbon and graphitematerials. When part of a rotor circuit, the brushes may be contained ina brush holder assembly that include springs which cause the brushes tomaintain firm contact with electrically conductive rotating portions ofa rotor. In a typical alternator, two slips rings are located on one endof the rotor assembly and are respectively connected to opposite ends ofthe rotor field winding. The corresponding pair of brushes is typicallypositioned to be urged by the springs against the rotating slip rings.

The rotor of an automotive alternator is typically driven by a belt andpulley system to rotate within stator windings coiled on a laminatediron frame. The magnetic field from the spinning rotor induces analternating current into the stator windings. The alternating current(AC) voltage is typically then converted to a direct current (DC)voltage by diode rectifiers that output the DC voltage to one or morebatteries and to electrical devices of a vehicle. Associated apparatusmay include a regulator and a controller for, among other things,monitoring battery voltage and current going to the field winding of therotor. The DC output voltage may be, for example, 14 volts, which isgenerally at least one volt more than a conventional vehicle's batteryvoltage, for example 12.7 volts. The field winding current forconventional automobile alternators may be as much as 5-8 amps, andambulances, buses, semi-tractors and various vehicles may require morecurrent, for example, for powering air-conditioning, heaters, lights,refrigeration units, etc. while a vehicle is idling.

Electrical communication between an electricity source and a brush maybe provided by a braided or twisted wire having one end connected to thebrush and the other end connected to the electrical source via one ormore electrical terminals. Such wire is often termed a shunt or shuntwire by those skilled in the art. Some conventional brushes have a shuntwire protruding from the rear of the brush through the center of aspring. This can be problematic because the shunt can tangle with thespring when the brush spring is compressed. A tangled shunt may causethe brush to become stuck, resulting in removal of field current fromthe alternator. In such a case, no electrical output is produced by thealternator. Other conventional brushes have a shunt protruding from thetop/bottom of the brush. However, with a non-symmetrical brush, such asa brush having an angled front contacting surface, this configuration isundesirable because the negative and positive brushes are required to bedifferent parts. For example, the shunt may protrude from the top of anegative brush and from the bottom of a positive brush.

SUMMARY

It is therefore desirable to obviate the above-mentioned disadvantagesby providing a brush holding assembly with shunt wires that do notbecome self-entangled and/or that do not become bent due to contact withthe sides of a shunt wire cavity. Conventional alternator brushstructures that exit respective shunt wires from the top and bottom, ina same general direction as the center shaft, add unwanted height to thecorresponding brush assembly, whereas the presently disclosedembodiments minimize overall brush assembly height by use of a pair ofside-exit brushes. Without further improvement, however, the use ofside-exit brushes may have a problem where the shunt wires have tightbends and become self-entangled. It is therefore an advantage of thedisclosed embodiments to provide sufficient space so that shunt wires donot have tight bends. The embodiments provide adjacent shunt wirecavities of sufficient size in order to maximize shunt wire space, whilestill providing an assembly that can use a single brush style in eitherbrush location. The embodiments described herein reduce or preventtangling, bending, and stressing (tension/torsion) of a shunt wire thatmay cause failure of an automotive alternator. For example, if a shuntwire becomes damaged, caught, bent, and/or self-entangled, it may becomecompressed and transfer the compression force to a brush, causing thebrush to become stuck. By implementing the disclosed structure, suchunwanted biasing of a brush and unwanted stressing of a shunt wire areprevented.

According to an embodiment, a brush holder assembly for an alternatorhaving a rotational axis includes a pair of brushes each having acontacting surface defining a width and a height, the height extendingin a direction approximately parallel to the rotational axis, and eachhaving a shunt wire extending laterally from the brush in the widthwisedirection. The brush holder assembly has a housing having first andsecond brush chambers, corresponding first and second wire cavities eachdefining a cavity height extending in a direction substantially parallelto the rotational axis, and first and second slots respectivelyinterposed between the corresponding chamber and cavity. The respectiveshunt wires extend through the first and second slots then through thefirst and second wire cavities. The cavity heights of the first andsecond wire cavities are each at least approximately 0.9 times theheight of one of the brushes.

According to an embodiment, the height of the first wire cavity is lessthan approximately 0.97 times ((A/2) plus B), where A is the brushheight and B is the distance between the brushes.

According to an embodiment, an alternator brush holder assembly definesperpendicular y and z axes, the z-axis extending substantially parallelto a rotational shaft of an alternator. The assembly includes first andsecond brushes each having a shunt wire protruding from a lateral sideof the brush, and a housing having: first and second brush chambers eachextending approximately parallel with the y-axis and having the firstand second brushes disposed therein; first and second wire cavitiesextending from a brush-forward portion to a wire exit portion, the firstwire cavity defining a centerline that extends in a direction forming anangle α with the z-axis; and first and second slots respectivelyconnecting the first and second wire cavities with the first and secondbrush chambers. The first and second shunt wires extend laterallythrough the respective first and second slots and then through therespective first and second wire cavities. The first wire cavity has az-axis dimension of Z, whereby the length of the first wire cavity isZ·(secant α).

According to an embodiment, a brush holder assembly for an alternatorhaving a rotational axis includes a pair of brushes each having acontacting surface defining a width and a height, the height extendingin a direction approximately parallel to the rotational axis, and eachhaving a shunt wire extending from the brush in the widthwise direction.The brush holder assembly includes a housing having first and secondbrush chambers, corresponding first and second wire cavities eachdefining a cavity height extending in a direction substantially parallelto the rotational axis, and first and second slots respectivelyinterposed between the corresponding chamber and cavity. The brushholder assembly includes a pair of springs disposed in respective onesof the brush chambers for biasing the brushes toward the respectivecontacting surfaces. The respective shunt wires extend through the firstand second slots then through the first and second wire cavities, thecavity heights of the first and second wire cavities are each at leastapproximately 0.9 times the height of one of the brushes, the height ofthe first wire cavity is less than approximately 0.97 times ((A/2) plusB), where A is the brush height and B is the distance between thebrushes, and the distance B is approximately the same as the height ofone of the brushes.

The foregoing summary does not limit the invention, which is defined bythe attached claims. Similarly, neither the Title nor the Abstract is tobe taken as limiting in any way the scope of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The above-mentioned aspects of exemplary embodiments will become moreapparent and will be better understood by reference to the followingdescription of the embodiments taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a schematic view of a portion of a conventional vehiclealternator that includes a brush assembly;

FIG. 2 is top view of a brush having a side-exit shunt wire;

FIG. 3 is a perspective view of a brush holder assembly;

FIG. 4 is a perspective view of a brush holder assembly according to anexemplary embodiment;

FIG. 5 is a perspective view of a brush holder assembly according to anexemplary embodiment;

FIG. 6 is a cutaway perspective view of the brush holder assembly ofFIG. 5;

FIG. 7 is another cutaway perspective view of the brush holder assemblyof FIG. 5; and

FIG. 8 is an enlarged front view of a brush holder according to anexemplary embodiment.

DETAILED DESCRIPTION

The embodiments described below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Rather, theembodiments are chosen and described so that others skilled in the artmay appreciate and understand the principles and practices of theseteachings.

FIG. 1 is an enlarged sectional schematic view of a portion of aconventional vehicle alternator that includes a brush assembly 1. Brushassembly 1 includes a housing 2 made of thermosetting resin and formedto have two separate brush chambers 3, 4 for accommodating correspondingbrushes 5, 6 therein. Constant force springs 7, 8 are respectivelylocated inside chambers 3, 4 for urging brushes 5, 6 outward so thatbrush contacting ends 21, 22 are in abutment with slip rings 118, 119attached to and concentric with the shaft 128. Slip rings 118, 119 areelectrically connected to opposite ends of the rotor coil (not shown) ofthe alternator. Brush 6 has a first shunt wire 9 electrically connectedthereto and extending from a shunt connection location 18 along a brushbottom surface 23, through a slot 19 and into a wire cavity 20.Similarly, brush 5 has a second shunt wire (not shown) electricallyconnected thereto at a shunt connection location 24 along a brush topsurface 25 and extending out into a wire cavity (not shown) that isseparate from wire cavity 20. A sealing member 26 may be provided atselected locations for preventing contamination of brush assembly 1. Inorder to vent dust and powder created by wearing of brushes 5, 6,ventilation holes 27 may be provided in housing 2 in locations where thevarious interior portions of brush assembly will still be protected frombecoming wet when the alternator is installed in a vehicle. The presentinventors have determined that shunt wire 9 may become entangled and/orbent when wire cavity 20 lacks sufficient space. In addition, brushes 5,6 respectively have top and bottom shunt configurations, whichnecessitates stocking two separate brushes. Further, installation ofbrushes 5, 6 may be difficult because the respective brush orientationsare different.

FIG. 2 shows a brush 30 having a body portion 31 and a shunt wire 32attached thereto at a shunt connection location 33 along lateral edge34. For example, brush 30 may be formed of graphite and/or carbon, andmay contain wear-resistant materials. Shunt wire 32 is typically formedof a woven copper braid. Spring engagement portions 36 are formed on therear end 37 of brush 30 so that brush 30 consistently mates with aspring when installed into a brush holder assembly. The distal end 35 ofshunt wire 32 may be terminated with a terminal or with a connector (notshown) for electrical communication with an electrical supply such as avehicle battery. Brush 30 may have an angled and/or curved frontcontacting surface 38 in order to reduce chatter that might otherwiseoccur when surface 38 is in contact with rotating slip rings. Brush 30may include a lubricant (not shown) for reducing and/or ameliorating thefriction between brush 30 and a slip ring of the alternator. Powder anddust created by such friction may be exhausted during operation, in aspace in front of the brushes. During operation in an automotivealternator, brush 30 wears very slowly and correspondingly travels veryslowly so that shunt wire 32 is slowly extended and is typically notlikely to experience fatigue under normal temperature conditions.

FIG. 3 illustrates an exemplary brush holder assembly 10, shown prior toinstallation of brushes 30. Brush assembly 10 has a body portion 11 madeof polyphenylene sulfide (PPS), polypropylenes comprising 20 to 40% oftalc as filler (PPT), and/or other plastics or copolymers or blendsthereof, and/or including nylon and/or a thermosetting polymer such asepoxy, polyimide, polyester, and the like. Since there is relativelylittle heat being internally generated in brush assembly 10, the plasticor other material of body 11 is typically specified for withstandingheat being generated from ancillary elements, for example rectifierdiodes. A pair of brush chambers 12, 13 is provided for accommodating acorresponding pair of brushes (not shown in FIG. 3) therein. Brushchambers 12, 13 are respectively connected to wire cavities 14, 15 viaslots 16, 17. Cavities 14, 15 each have a symmetrical profile with acavity height of 3.7 mm measured, for example, from the centerline 39 ofthe shunt connection 33, corresponding to a midpoint of slot 16, to oneend 40 of cavity 14 and represented in FIG. 3 as end line 41. In such acase, the distance between the top 42 and bottom 43 ends of each cavity14, 15 is typically 7.4 mm, and wire cavities 14 and 15 are thus ofapproximately the same height. In this symmetrical form, top 42 andbottom 43 ends of cavity 15 are each equidistant from centerline 39.When assembled, brush assembly 10 has two brush portions 30 each havinga respective shunt wire 32 protruding from a lateral side of the brushand extending laterally into a shunt wire cavity 14, 15 via slot 16, 17.As noted below, the height dimension relates generally to the Z-axis.The cavity heights (in a direction paralleling the Z-axis) of the wirecavities 14, 15 are each at least approximately 0.9 times the height ofa brush 30 slidably received in brush chamber 12 or 13, as shown in FIG.3, where it can also be seen that the distance between brushes 30received into brush chambers 12, 13 is approximately the same as theheight of one of the brushes. For each of the brush portions, therespective heights of the slot and cavity are centered with a centerlineof the shunt wire connection to the side of the brush. Although suchstructure may allow the same ‘lateral edge shunt’ type brush 30 to beused in both cavities 14, 15 and there are no tangling problems with aspring, brush assembly 10 may still be subject to failure fromself-tangling and/or bending of shunt wires 32. Such tangling and/orbending may be caused by the extreme vibrations that can occur in anenvironment of an automotive alternator, and the vibration may causesbrushes 30, and shunt wires 32, to bounce. This dynamic vibration effectmay result in increasing torsion of a brush 30 when shunt wire 32 isbound, kinked, or otherwise restrained.

As shown in FIG. 2, the width dimension and a lateral or sidewaysdirection relate to the X-axis of brush 30, and the depth dimensionrelates generally to the Y-axis of brush 30. The height dimensionrelates generally to the Z-axis, shown by example in FIG. 1 being inparallel with the center axis of an alternator shaft 128. Typically, thelength of a shunt wire cavity refers to the longest dimension in across-sectional view, or a portion thereof.

FIG. 4 illustrates an exemplary brush holder assembly 50 having a bodyportion 44 made of materials described above for body portion 11, shownprior to installation of brushes. A pair of brush chambers 45, 46 isprovided for accommodating a corresponding pair of brushes (not shown inFIG. 4) therein. Brush chambers 45, 46 are respectively connected towire cavities 47, 48 via slots 28, 29. Wire cavity 47 has anasymmetrical profile with a cavity height of at least 7.5 mm measuredfrom centerline 51 of the shunt connection 33, corresponding to themidpoint of slot 28, to the top end 53 of cavity 47, represented in FIG.4 as end line 49. Wire cavity 48 has an asymmetrical profile with acavity height of at least 7.5 mm measured from centerline 52 of theshunt connection 33, corresponding to the midpoint of slot 29, to thetop end 54 of cavity 48 and represented in FIG. 4 as end line 55. Whenwire cavities 47, 48 have the same height, the distance, for example,between the top 54 and bottom 56 ends of cavity 48, and between the top53 and bottom 57 ends of cavity 47 are each typically 8.5 mm, and wirecavities 47 and 48 are thus of approximately the same height. Whenassembled, brush assembly 50 has two brush portions each having arespective shunt wire 32 protruding from a side of the brush andextending laterally into a shunt wire cavity 47, 48 via slot 28, 29. Theextra room provided by the asymmetrical cavity arrangement greatlyreduces the dynamic effects of vibration, as evidenced by environmentaltesting. As noted above, the height dimension relates generally to theZ-axis. The cavity heights (in a direction paralleling the Z-axis) ofthe wire cavities 47, 48 are each at least approximately 0.9 times theheight of a brush 30 slidably received in brush chamber 45 or 46, asshown in FIG. 4, where it can also be seen that the distance betweenbrushes 30 received into brush chambers 47, 48 is approximately the sameas the height of one of the brushes.

FIG. 5 shows a brush assembly 60 having a brush 30 enclosed in eachbrush chamber 58, 59. Each brush chamber 58, 59 has a rounded topportion 61 and a rounded bottom portion 62 (see, e.g., FIG. 6) so thatsprings 69, 70 may be installed prior to installing brushes 30. Thecontacting surfaces 38 of respective brushes 30 may be angled and/orcurved (e.g., FIG. 2), and the outer face 63 of housing 64 may beangled/curved in correspondence with the shapes of such contactingsurfaces 38. The springs urge brushes 30 outward and into engagementwith the slip rings of an alternator, and brush chambers 58, 59 areformed to allow brushes 30 to easily slide outward of surface 63 as theywear from friction. Shunt wires 32 of brushes 30 extend laterallythrough respective slots 65, 66 into respective wire cavities 67, 68.Since wire cavities 67, 68 are each disposed to one widthwise side ofbrush chambers 58, 59, brushes 30 having an angled contacting surfacemay be used in either brush chamber, thereby eliminating the need forstocking and installing two separate brushes. Each wire cavity 67, 68extends essentially in only one height-wise direction, thereby reducingtangling of the corresponding shunt wires 32 while minimizing theoverall height of housing 64. The shunt wires 32 move more easily in theone-sided cavities 67, 68, which allow for efficient packing of therespective shunt wires 32 during brush travel. The resultant reductionin binding and in tension on shunt wires 32 also facilitates the smoothmovement of brushes 30 because such reduces lateral forces being appliedto brushes 30. Shunt wire 32 of the top brush 30 exits the top ofhousing 64, and shunt wire 32 of the bottom brush 30 exits the bottom ofhousing 64, as shown by example in FIG. 6.

FIG. 5 and FIG. 7 are cutaway views of an exemplary brush assembly 60.Constant force springs 69, 70 fit inside respective brush chambers 58,59 and are configured to expand and contract therein. The diameter ofsprings 69, 70 is typically selected to minimize vibration or unintendedmovement during alternator operation, while also assuring freedom ofspringing movement. Springs 69, 70 mate with spring engagement portions36 (e.g., FIG. 2) of brushes 30 to urge brushes 30 into engagement withthe slip rings. Respective heights 71, 72 of slots 65, 66 are sufficientto allow respective shunt wires 32 to slide there-along but not so greatas to provide a possibility of shunt wires 32 coming in contact withexposed spring portions 73, 74. During installation, the respective ends35 of shunt wires 32 are inserted into exit holes 77, 78, and may begrasped gently at respective bend locations 75, 76 to insure uniformityof wire routing through cavities 67, 68 when bends 75, 76 are placed ata predetermined location. Bends 75, 76 are typically gradual in shape toavoid kinking and may be pre-formed. Wire cavity 67 has an asymmetricalprofile with a cavity height of at least 7.5 mm—measured from centerline79 of the shunt connection 33, corresponding to the midpoint of slot 65,to the top end 81 of cavity 67, represented in FIG. 7 as end line 80.Wire cavity 68 has an asymmetrical profile with a cavity height of atleast 7.5 mm—measured from centerline 82 of the shunt connection 33,corresponding to the midpoint of slot 66, to the top end 84 of cavity 68and represented in FIG. 7 as end line 83. The distance between the top81 and bottom 85 ends of cavity 67, and between the top 84 and bottom 86ends of cavity 68 are each typically at least 8.5 mm. Tapered portions114, 115 help guide the two respective shunt wire ends 35 toward shuntexit holes 77, 78 during assembly. The length of a shunt wire cavity maytherefore be referred-to as being a nominal value, because such taperedportions have a cavity length in the height-wise direction thatdecreases as the cavity approaches the respective wire exit port 120,122. In order to maximize the available cavity room, the portion of body44 between cavities 67, 68 is typically minimized.

The embodiment of brush assembly 60 may be generically described ashaving a pair of essentially single-sided asymmetrical wire cavities 67,68, each having a z-axis height (measured, for example, from thecenterline 79 of the shunt-brush connection 33 to the long end 81 of thecavity) that is at least 0.9 times the z-axis height of brush 30. Sothat bottom cavity 68 does not run into top cavity 67, the height ofbottom cavity 68 (for a bottom wire cavity extending parallel to thez-axis) is typically less than 0.97 times (half the z-axis height ofbrush 30, plus the z-axis height between the two brushes 30). Since itis desirable to maintain a distance of approximately one brush heightbetween the two brushes 30, the upper limit for the height of bottomwire cavity 68 (when extending in parallel with the z-axis) becomes 1.45times the height of brush 30.

FIG. 8 is a front view of an exemplary brush holder assembly 90, shownbefore installation of brushes and springs into brush chambers 87, 88.Brush chambers 87, 88 are respectively connected to wire cavities 91, 92via slots 93, 94. Wire cavities 91, 92 are each formed to be skewed atleast with respect to z-axis 98. As shown, wire cavity 91 has acenterline 89 that extends at an angle α away from z-axis 98. Wirecavity 92 has a centerline 103 that extends at an angle β away fromz-axis 98. Each wire cavity 91, 92 is defined by a surrounding volume ofmaterial integrally formed with body portion 97 that insulates thecavity spaces, and such surrounding material includes, for example, abarrier 100 formed at the end portion 99 of wire cavity 91. By formingwire cavity 91 at the skewed angle α, the distal end 104 of wire cavity91 remains at a z-axis location 101 (c.f., embodiment of FIG. 5, shownas dashed portion 105), but the wire cavity length increases from thez-dimension 106 to the skewed wire cavity length 107. For example, whenthe length 106 measured from the centerline 102 (shown as the x-axis) ofthe brush-shunt connection 33 (e.g., FIG. 2) to the z-axis location 101is Z, the skewed cavity length 107 from the intersection of z-axis 98and x-axis 102 to the distal end 104 of wire cavity 91 is (Z·(secantα)). Thereby, the skewing of wire cavity 91 by an angle α substantiallyfurther increases the length thereof. For example, when Z=7.5 mm andα=30 degrees, the skewed cavity length 107 becomes (7.5·(secant 30))=8.7mm. The same general analysis applies to the skewing of centerline 103of cavity 92 at an angle β away from z-axis 98. Body portion 97 may bemodified to reduce the body size by slanting a body portion 108 adjacentwire cavity 91 and by slanting a body portion 109 adjacent wire cavity92, thereby removing significant body material and providing associatedcost and space savings. Bottom shunt wire exit port 96 is locatedadjacent a bottom surface 110 of body portion 97. Top shunt wire exitport 95 may be located along an intermediate surface 112 provided by theskewing of wire cavity 92 and associated slanting of body portion 109.In such a case, an electrical terminal 113 for electricallycommunicating with a brush of brush chamber 87 may be located alongintermediate surface 112 in proximity to wire exit port 95.Alternatively, wire exit port 95 may be located along body portion 108or in proximity to a body top surface 111. By the described principles,an artisan may choose to provide a shunt wire exit for brush chamber 87in either the same or in a generally opposite direction as the directionof wire exit port 95.

The various embodiments may advantageously enclose the portions of thewire cavities and the slots which are otherwise open along the brushcontacting end of the body portion. For example, after brushes 30 havebeen installed, shunt wire ends 32 have been fed out of the wire exits,and the shunt wires 32 have been properly positioned within the wirecavities, the wire cavities and slots opening toward the brush contactend may be plugged such as by installing a seal, epoxy, or othermaterial. Such plugging may keep unwanted brush powder, generated byfriction of brushes 30 with the slip rings, and other debris, fromentering the wire cavities. Alternatively, the body portion may bemolded to eliminate these external openings for preventing exposure ofthe wire cavities near the brushes.

Various features and structure of exemplary brush assemblies 50, 60, 90,are not exclusive to the illustrated embodiments but may be selectivelycombined where appropriate for a given application. A brush holderassembly for a given application may be formed, in whole or in part, inany appropriate manner.

While various embodiments incorporating the present invention have beendescribed in detail, further modifications and adaptations of theinvention may occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe spirit and scope of the present invention.

What is claimed is:
 1. A brush holder assembly for an alternator havinga rotational axis, comprising: a pair of brushes each having acontacting surface defining a width and a height, the height extendingin a direction approximately parallel to the rotational axis, and eachhaving a shunt wire extending laterally from the brush in the widthwisedirection; and a housing having first and second brush chambers,corresponding first and second wire cavities each defining a cavityheight extending in a direction substantially parallel to the rotationalaxis, and first and second slots respectively interposed between thecorresponding chamber and cavity; wherein the respective shunt wiresextend through the first and second slots then through the first andsecond wire cavities, and wherein the cavity heights of the first andsecond wire cavities are each at least approximately 0.9 times theheight of one of the brushes.
 2. The alternator brush holder assemblyaccording to claim 1, wherein the height of the first wire cavity isless than approximately 0.97 times ((A/2) plus B), and wherein A is thebrush height and B is the distance between the brushes.
 3. Thealternator brush holder assembly according to claim 2, wherein themaximum distance between opposing surfaces, for the first wire cavity,is approximately 1.45 times the height of the brush.
 4. The alternatorbrush holder assembly according to claim 1, wherein the first and secondwire cavities have approximately the same heights.
 5. The alternatorbrush holder assembly according to claim 4, wherein the distance betweenthe brushes is approximately the same as the height of one of thebrushes.
 6. The alternator brush holder assembly according to claim 1,further comprising a pair of springs disposed in respective ones of thebrush chambers for biasing the brushes toward the respective contactingsurfaces.
 7. The alternator brush holder assembly according to claim 1,wherein the respective heights of the first and second wire cavities,measured from the centerline of connection between shunt wire and brush,are approximately 7.5 mm.
 8. The alternator brush holder assemblyaccording to claim 1, wherein the respective heights of the first andsecond wire cavities extend primarily only in one height-wise directionaway from the respective slots.
 9. A brush holder assembly for analternator having a rotational axis, comprising: a pair of brushes eachhaving a contacting surface defining a width and a height, the heightextending in a direction approximately parallel to the rotational axis,and each having a shunt wire extending from the brush in the widthwisedirection; a housing having first and second brush chambers,corresponding first and second wire cavities each defining a cavityheight extending in a direction substantially parallel to the rotationalaxis, and first and second slots respectively interposed between thecorresponding chamber and cavity; and a pair of springs disposed inrespective ones of the brush chambers for biasing the brushes toward therespective contacting surfaces; wherein the respective shunt wiresextend through the first and second slots then through the first andsecond wire cavities; wherein the cavity heights of the first and secondwire cavities are each at least approximately 0.9 times the height ofone of the brushes; wherein the height of the first wire cavity is lessthan approximately 0.97 times ((A/2) plus B), wherein A is the brushheight and B is the distance between the brushes; and wherein thedistance B is approximately the same as the height of one of thebrushes.